Such a method and related devices are already known in the art, e.g. from “3rd Generation Partnership Project; Technical Specification Group Core Network; IP Multimedia (IM) Session Handling; IP Multimedia (IM) call model; Stage 2 (Release 5) with reference 3GPP TS 23.218 V5.2.0 (2002-09)”. This document is published by the 3rd Generation Partnership Project (3GPP) in September 2002.
Especially Annex C of this document, discloses an example for activating Application Servers using filter criteria for triggering an Application Server, i.e. the way Application Servers are selected and respectively invoked by the Call Session Control Function based on the content of filter criteria.
An incoming call to a particular user is intercepted by the call control network element, called the Call Session Control Function, which is in charge of serving the called user. The Call Session Control Function Network Element has been pre-configured with this user's triggering data. When trigger conditions, called filter criteria, are met a certain Application Server is to be contacted and will receive the control of this incoming call. Several Application Servers can be contacted in sequence in a certain call.
The triggering conditions describe a list of filter criteria each being linked to an application server for executing a corresponding Application service. For a number of specific cases to be described in the filter criteria a specific application is automatically pre-selected based on the triggering data for taking the control of the incoming call.